For retracting gingiva from a prepared tooth a cord can be used. In this respect, a retraction cord is packed between gingival tissue and the margin of the prepared tooth using an appropriate dental instrument e.g. a Heinemann spatula. To obtain sufficient vertical and horizontal retraction of gingival tissue, it is often necessary to pack several lengths of retraction cord into the sulcus in order to be able to make a detailed dental impression. A description of the background in regard to retraction cords can be found e.g. in U.S. Pat. No. 4,522,593.
Generally, dental retraction cords are sometimes difficult to place into the gingival sulcus. The procedure can also be time consuming. It can also be cumbersome to remove the retraction cord prior to taking the impression. Coagulated blood may adhere to the cord and removing it may open the wound again which results in bleeding.
For a more convenient placement retraction pastes have been suggested.
US 2005/0287494 and EP 1 611 876 A1 describe non-hardening pastes with a defined viscosity containing fibrillated fibers, filler(s), adstingent(s) and water.
U.S. Pat. No. 5,362,495 describes an injectable non-hardening paste. The paste can be delivered with a application device described in U.S. Pat. No. 6,170,714.
US 2004/0106086 describes an impression material that is used for retraction of gingival tissue.
US 2005/0260543 describes silicone based materials in which astringents are incorporated. This material is essentially used in a two-step technique. A two step technique in which two types of material applied and hardened subsequently in the patients mouth is time consuming for both dentist and patient. A two-step procedure is also uncomfortable for the patient.
WO 2006/007780 refers to a biologically activated injection bone reconstruction gel. It is stated that this material can be applicable in fractures, slow healing fractures, bone defects reconstruction, orthopedic surgery and dental diseases. The material is prepared from two components, wherein water is used as a main ingredient. The concentration of alginate in the aqueous composition is within a range of 1 to 4%.
US 2005/0069838 discloses a dental kit and method for retraction sulcus using an expanding silicone compound or mixture of different silicone compounds. However, silicone compounds are inorganic and hydrophobic nature, thus having limited biocompatibility with oral tissue and disadvantages in flowing to moist tissue and tooth surfaces and moist areas like the gingival sulcus.
Dental alginate impression materials are usually delivered in a powdery form which can form an irreversible hydrocolloide in the presence of water. The powder usually contains potassium or sodium alginic acid, filler(s), retarder(s) and additives. The pastes are made either by hand-mixing the powder and water or by using special mixing devices. All dental alginate impression materials usually have a high filler content (generally above about 60 wt. -% with respect to the whole composition in dry form, that is, before water is added). Despite of this high filler content the impression materials have limited tensile strength because of their gel-like consistency after curing and thus are not suitable for use as a retraction material.
A commercially available retraction composition is sold under the name Expasyl™. According to the instruction of use, the viscosity of the composition changes when water is absorbed. However, a reduction in viscosity is sometimes undesirable since having high consistency is one pre-requisite for applying force onto the gingiva for sufficient retraction.
Known retraction devices are often not biocompatible and can thus be tissue irritating.
A further general disadvantage of commercially available pastes used for dental retraction is that the paste cannot be placed cord-like into the gingival sulcus having the result that sometimes the whole prepared tooth is covered with the paste. This prevents pushing the paste deeper into the gingival sulcus using a dental tool like a spatula.
In general, removing of non-hardening pastes before taking the impression is not optimal. Usually it is rinsed off with water. During this procedure there is a risk that residues of paste may remain in the sulcus. These residues may prevent the impression material from flowing into the sulcus area and may negatively influence the setting of the impression material which is applied subsequently. After rinsing off the paste with water and additional drying step is required before the impression can be taken.
Hardening materials are easier to remove. However, they are not very hydrophilic. This might cause problems in regard to flowability of the material into the gingival sulcus.
Therefore, a hydrophilic curable paste would be desirable.
Thus, it is an object of the invention to provide a paste which can be used for retraction of oral tissue especially prior to impression taking. Ideally, the paste cures in the patient's mouth in a reasonable amount of time.